你需要知道的20个常用的Python技巧

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2021-06-09 00:01


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本文转自|机器学习算法那些事
Python的可读性和简单性是其广受欢迎的两大原因,本文介绍20个常用的Python技巧来提高代码的可读性,并能帮助你节省大量时间,下面的技巧将在你的日常编码练习中非常实用。


1.字符串反转



使用Python切片反转字符串:

# Reversing a string using slicing

my_string = "ABCDE"
reversed_string = my_string[::-1]

print(reversed_string)

# Output
# EDCBA


2.每个单词的第一个字母大写



使用title函数方法:

my_string = "my name is chaitanya baweja"

# using the title() function of string class
new_string = my_string.title()

print(new_string)

# Output
# My Name Is Chaitanya Baweja


3. 字符串查找唯一元素



使用集合的概念查找字符串的唯一元素:

my_string = "aavvccccddddeee"

# converting the string to a set
temp_set = set(my_string)

# stitching set into a string using join
new_string = ''.join(temp_set)

print(new_string)

# output
# cdvae


4.重复打印字符串和列表n次



你可以使用乘法符号(*)打印字符串或列表多次:

n = 3 # number of repetitions

my_string = "abcd"
my_list = [1,2,3]

print(my_string*n)
# abcdabcdabcd

print(my_list*n)
# [1,2,3,1,2,3,1,2,3]


5.列表生成



# Multiplying each element in a list by 2

original_list = [1,2,3,4]

new_list = [2*x for x in original_list]

print(new_list)
# [2,4,6,8]


6.变量交换



a = 1
b = 2

a, b = b, a

print(a) # 2
print(b) # 1


7.字符串拆分为子字符串列表



使用.split()函数:

string_1 = "My name is Chaitanya Baweja"
string_2 = "sample/ string 2"

# default separator ' '
print(string_1.split())
# ['My', 'name', 'is', 'Chaitanya', 'Baweja']

# defining separator as '/'
print(string_2.split('/'))
# ['sample', ' string 2']


8.多个字符串组合为一个字符串



list_of_strings = ['My', 'name', 'is', 'Chaitanya', 'Baweja']

# Using join with the comma separator
print(','.join(list_of_strings))

# Output
# My,name,is,Chaitanya,Baweja


9.检测字符串是否为回文



my_string = "abcba"

if my_string == my_string[::-1]:
print("palindrome")
else:
print("not palindrome")

# Output
# palindrome


10. 统计列表中元素的次数



# finding frequency of each element in a list
from collections import Counter

my_list = ['a','a','b','b','b','c','d','d','d','d','d']
count = Counter(my_list) # defining a counter object

print(count) # Of all elements
# Counter({'d': 5, 'b': 3, 'a': 2, 'c': 1})

print(count['b']) # of individual element
# 3

print(count.most_common(1)) # most frequent element
# [('d', 5)]


11.判断两个字符串是否为Anagrams



Anagrams的含义为两个单词中,每个英文单词(不含大小写)出现的次数相同,使用Counter类判断两个字符串是否为Anagrams。

from collections import Counter

str_1, str_2, str_3 = "acbde", "abced", "abcda"
cnt_1, cnt_2, cnt_3 = Counter(str_1), Counter(str_2), Counter(str_3)

if cnt_1 == cnt_2:
print('1 and 2 anagram')
if cnt_1 == cnt_3:
print('1 and 3 anagram')

# output
# 1 and 2 anagram


12. 使用try-except-else-block模块



except获取异常处理:

a, b = 1,0

try:
print(a/b)
# exception raised when b is 0
except ZeroDivisionError:
print("division by zero")
else:
print("no exceptions raised")
finally:
print("Run this always")

# output
# division by zero
# Run this always


13. 使用枚举函数得到key/value对



my_list = ['a', 'b', 'c', 'd', 'e']

for index, value in enumerate(my_list):
print('{0}: {1}'.format(index, value))

# 0: a
# 1: b
# 2: c
# 3: d
# 4: e


14.检查对象的内存使用情况



import sys

num = 21

print(sys.getsizeof(num))

# In Python 2, 24
# In Python 3, 28


15.合并字典



dict_1 = {'apple': 9, 'banana': 6}
dict_2 = {'banana': 4, 'orange': 8}

combined_dict = {**dict_1, **dict_2}

print(combined_dict)
# Output
# {'apple': 9, 'banana': 4, 'orange': 8}


16.计算执行一段代码所花费的时间



使用time类计算运行一段代码所花费的时间:

import time

start_time = time.time()
# Code to check follows
for i in range(10**5):
a, b = 1,2
c = a+ b
# Code to check ends
end_time = time.time()
time_taken_in_micro = (end_time- start_time)*(10**6)

print(time_taken_in_micro)

# output
# 18770.217895507812


17. 列表展开



from iteration_utilities import deepflatten

# if you only have one depth nested_list, use this
def flatten(l):
return [item for sublist in l for item in sublist]

l = [[1,2,3],[3]]
print(flatten(l))
# [1, 2, 3, 3]

# if you don't know how deep the list is nested
l = [[1,2,3],[4,[5],[6,7]],[8,[9,[10]]]]

print(list(deepflatten(l, depth=3)))
# [1, 2, 3, 4, 5, 6, 7, 8, 9, 10]


18. 列表采样



import random

my_list = ['a', 'b', 'c', 'd', 'e']
num_samples = 2

samples = random.sample(my_list,num_samples)
print(samples)
# [ 'a', 'e'] this will have any 2 random values


19.数字化



将整数转化成数字列表:

num = 123456

# using map
list_of_digits = list(map(int, str(num)))

print(list_of_digits)
# [1, 2, 3, 4, 5, 6]

# using list comprehension
list_of_digits = [int(x) for x in str(num)]

print(list_of_digits)
# [1, 2, 3, 4, 5, 6]


20.检查列表元素的唯一性



检查列表中每个元素是否为唯一的:

def unique(l):
if len(l)==len(set(l)):
print("All elements are unique")
else:
print("List has duplicates")

unique([1,2,3,4])
# All elements are unique

unique([1,1,2,3])
# List has duplicates

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